The present invention relates to a machining device such as a portable circular saw, a desktop circular saw, or a grooving cutter, and to an electric motor that can be suitably used in this machining device.
The electric motor constituting a drive source of a machining device of this type is, for example, an inner rotor type electric motor in which a rotor is arranged on the inner peripheral side of a stator, or an outer rotor type electric motor in which a rotor is arranged on the outer peripheral side of a stator. As compared with the inner rotor type electric motor, the outer rotor type electric motor exhibits a rotor of a larger surface area, so that it is possible to set the magnetic force large, whereby it can output high torque. Thus, if the output torque set is the same, the outer rotor type motor can be smaller in size as compared with the inner rotor type motor. If the two types of motor are set to an equal size, the outer rotor type motor can output higher torque as compared with the inner rotor type motor.
Japanese Laid-Open Patent Publication No. 2012-176468 discloses a machining device using an outer rotor type electric motor as a drive source. The outer rotor type electric motor includes a stator and a motor shaft passing through the stator. The stator has one end situated on an output side in a motor axis direction and the one end is fixed to a case via a stator base. A rotor and a cooling fan are supported on an end of the motor shaft near the other end of the stator. A driving gear of a reduction gear train is attached to the other end of the motor shaft and situated on the output side. A rotational power of the electric motor is transmitted to a spindle through mesh-engagement between the driving gear and a driven gear, whereby a rotary cutting tool rotates. A motor housing accommodating the electric motor is connected to a gear housing accommodating the reduction gear train. The gear housing is provided integrally on the back of a blade case.
There has been a need for an improvement of the outer rotor type electric motor mainly in terms of dismantling property and assembling property. The stator is attached to the stator base at a position nearer to the blade than the rotor. The stator base and the motor housing are connected to the gear housing together by a screw. That is, the stator base is not directly fixed to the gear housing. Thus, when the motor housing is removed at the time of the dismantling of the electric motor, the stator base is also removed. And, the stator is separated from the motor housing and the stator base, and the stator is attracted to a magnet of the rotor to be integrated therewith. The magnetic force of the magnet of the rotor is large, so that in the state in which the stator not connected to the motor housing and the rotor are attracted to each other as stand-alone units, the operation of separating the two from each other against the magnetic force is very difficult to perform.
Thus, there has been a need for an outer rotor type electric motor of high dismantling property and high maintenance property, which is realized, for example, by enabling the stator and the rotor to be easily separated from each other at the time of dismantling of the electric motor.